CAIRO, Egypt — Bustling cities throughout the Middle East fell eerily quiet Tuesday on the first day of Ramadan.

In much of the Islamic world, religious officials announced spotting the first sliver of the crescent moon Monday night, signaling the start of the holy month.

Muslims hurried home Tuesday for “iftar,” the meal that breaks the dawn-to-dusk fast. For the coming four weeks, Muslims are expected to abstain during daylight hours from food, drink, smoking and sex to focus on spiritual introspection.

In Baghdad, the first day of Ramadan for minority Sunnis was marred by a car bomb at the main entrance to the heavily fortified Green Zone, a district of Iraqi government buildings and the U.S. and British Embassies. The powerful blast killed two policemen.

Al-Qaida in Iraq has issued a call for its followers to step up attacks against U.S. and Iraqi forces and make it a “month of victory for Muslims and a month of defeat for the hypocrites and polytheists.”

Dying for a holy cause?Previous Ramadans since the 2003 U.S.-led invasion of the country have seen a spike in violence — especially suicide attacks — in part because some Islamic extremists believe those who die in combat for a holy cause during the period are especially blessed.

“People fear car bombs, kidnapping and theft. The streets are empty,” said Marwan Hamid, a shopkeeper in Baghdad’s Shorja food market, who complained few people were out shopping.

Shiite Muslims, the majority sect in Iraq, begin fasting on Wednesday as do co-religionists in neighboring Iran. Oman also begins Ramadan on Wednesday.

Elsewhere, the first night of Ramadan was marked with special meals, sweets and charity giving to the poor and homeless.

In Cairo, traffic jammed the streets in mid-afternoon as people headed home for iftar. Under a bridge in the affluent neighborhood of Zamalek — and in other areas across Cairo — tables were set up outdoors by local businessmen to feed the needy. By the end of evening prayers, few cars were moving, as people sat down to special meals at home or in public squares.

Warnings from EgyptThere was some tension in Egypt, however, after an Islamic group that previously claimed responsibility for this summer’s attacks at Sharm el-Sheik vowed to launch an all-out war against Israelis, Americans and Egyptian police. An Egyptian security official said security was high across the country. He spoke on condition of anonymity because he is not authorized to talk to the press.

Israel has urged its citizens not to travel to Egypt’s Sinai peninsula during the Jewish New Year holiday, which began on Monday, because it said Arab militants were planning to kidnap Israeli tourists there.

Iranians don’t begin their fast until Wednesday, but families were busy shopping for dates and “zoulbia” and “bamiye” — special holiday sweets — for the first evening Ramadan meal.

One secondary school reminded passers-by of the season with a banner that read: “You are welcome to be God’s guest in the fasting month.” Students’ essays about the holy month were posted on one outside wall. “Let’s purify our soul by refusing to eat and drink from dawn to dusk,” one student urged.

Kuwaitis set up so-called Ramadan tents to entertain guests, hiring singers and making food and juice plentiful late into the night. Businesses adjusted their hours to open an hour or two later in the morning to allow residents to rest after a pre-dawn meal.

High tensions in LebanonIn Lebanon, which is 60 percent Muslim, Ramadan comes at a time of high tension as a U.N.-mandated probe into former Prime Minister Rafik Hariri’s assassination nears its end. The Lebanese fear the continuation of a series of bombings that have rattled the country since Hariri was killed.

Nevertheless, the bustling sidewalk cafes, restaurants and shops in downtown Beirut were jammed with local residents and tourists from other Mideast countries who come to dine, smoke water pipes or just stroll through the district.

Amman, the Jordanian capital, came to a standstill at sundown, with virtually all businesses closed. People crowded Amman restaurants for a meal to break the fast, as coffee shops prepared traditional apricot and tamarind juices, walnut-stuffed pancakes and water pipes for customers.

Muslims believe God began to reveal the Quran to the Prophet Muhammad more than 1,400 years ago during Ramadan.